1. Field of the Invention
This invention relates to a duplex communication wireless, and more particularly to a duplex communication wireless for use in a relatively short range of the type wherein the sum or difference component between a transmission frequency and a reception frequency is an intermediate frequency of a receiver.
2. Description of the Prior Art
An example of a duplex communication wireless is disclosed in Japanese Patent Laid-Open No. 109328/1986. This prior art discloses a circuit construction wherein part of the transmission signal outputted from a modulator disposed in a transmitter is supplied to a frequency mixer disposed in a receiver, and a reception signal which is received by an antenna and amplified by a high frequency amplifier is supplied to the frequency mixer in order to extract a signal of an intermediate frequency component obtained as the difference signal between the transmission frequency and the reception signal through the frequency mixer and a band-pass filter, and to reproduce a signal wave by demodulating the signal of this intermediate frequency component. In the duplex communication wireless of the kind described above, a duplex filter (hereinafter referred to as a "filter") is disposed between the antenna and the receiver so as to prevent the high output transmission signal supplied from the transmitter to the antenna from mixing with the reception signal received by the antenna and flowing into the receiver, as is obvious from the reference described above.
However, in the duplex communication wireless having the construction described above, a crystal filter having excellent frequency characteristics is necessary as the filter described above and since a frequency mixer consisting generally of active devices is necessary, it is difficult to reduce the production cost, size and weight of the wireless. Particularly in the case of a duplex communication wireless for a short range communication such as a toy-like wireless, the filter and frequency mixer described above render a critical problem for reducing the production cost, size and weight of the wireless.